1. Field of Invention
The present invention relates to a luminescent device, and particularly to an organic electro-luminescent device.
2. Description of the Related Art
Organic electro-luminescent device (OELD) is a component using the self-luminescent characteristic of the organic functional material to reach the display effects, wherein the organic functional material is divided into two types including small molecule OELD (SM-OELD) and polymer electro-luminescent device (PELD) according to its the molecular weight. The luminescent structures of both are comprised with a couple of electrodes and an organic functional layer. The structure related to the conventional organic electro-luminescent device is described as follows.
FIG. 1 is a schematic diagram illustrating the structure of conventional organic electro-luminescent device. Referring to FIG. 1, the conventional organic electro-luminescent device 100 comprises a substrate 110, an anode layer 120, an organic functional layer 130, and a cathode layer 140, wherein the anode layer 120 is disposed on the substrate 110 and the material of the anode layer 120 is indium tin oxide (ITO). The organic functional layer 130 is disposed on the anode layer 120 and the organic functional layer 130 is usually formed of several layers of organic films. Besides, the cathode layer 140 is disposed on the organic functional layer 130 and the material of the cathode layer 140 is generally metals.
When a DC voltage is applied, the holes are injected from the anode layer 120 into the organic functional layer 130 and the electrons are injected from the cathode layer 140 into the organic functional layer 130. Because of the voltage difference resulted from the applied electric field, the two carriers, holes and electrons, move in the organic functional layer 130 and produce radiative recombination. A part of the energy released by the recombination of the holes and electrons can excite the molecules of the organic luminescent material into single excited state molecules. When the single excited state molecules release energy and come back to the ground state, a portion of energy is released to luminesce as photons. The above-mentioned description is the luminescent theorem of the conventional organic electro-luminescent device 100.
However, the problem existed in the conventional organic electro-luminescent device 100 is that the light emitted by the organic functional layer 130 usually causes reflection or refraction because of the difference of the refractive index in each layer of the device. Therefore, most of the light emitted from the organic functional layer 130 is constrained within the device and not be able to pass through the substrate 110 so that the efficiency of luminescence of the organic electro-luminescent device 100 is decreased. In addition, the conventional organic electro-luminescent device 100 can only luminese on single side instead of double sides.